Answer:
0.66*10^-6m
Step-by-step explanation:
We know that the bright fringes are placed on the screen as follows
Ym= m*(lambda xL/d)
But we are given
L= 5.05
Deta Y= 1.59
d = 0.21
1.59* 10^-2m= lambda * 5.05m/2.1*10^-4m
So lambda=
1.59* 10^-2m x 2.1*10^-4m/ 5.05m
= 0.66*10^-6m